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68k memory and IO manager
[emu68 library documentation.]

Detailed Description

Handling memory and I/O access.

EMU68 memory manager assumes that all addresses in the lowest half part of address space are memory access. A simple bit test over most signifiant bit (23) of address allow to choose beetween memory or eventual IO access. In case of memory access, address is masked to fit available 68K onboard memory. Overflow does NOT generate address error. IO access are performed towards quick access tables. There are 6 acccess tables: for each read and write access in 3 sizes (byte, word and long). Each of this 6 tables has 256 entries filled with a pointer to suitable function. At init time, the entries of all tables are initialized to access 68K onboard memory. When an IO is plugged by user, it is mapped somewhere in 68K address space. EMU68 memory manager get bit 8 to 15 of address to make an index to be used in the suitable table (R/W for B/W/L).


  • Onboard memory byte, word and long read/write access.
  • Optimized IO warm mapping/unmapping.
  • Optionnal (compile time) enhanced memory control with RWX access tag and hardware breakpoints.


  • For optimization purposes IO must be mapped in high half memory (bit 23 of address setted).
  • Two IO can not shared the same memory location for bit 8 to 15. Conflicts could be resolved by creating an intermediate IO which dispatches to others. This mechanism has not been implemented yet, so users must do it them self if needed.

Atari-ST & Amiga IO areas

  • FF8800-FF88FF : YM2149 (ST)
  • FF8900-FF89FF : Micro-Wire (STE)
  • FF8200-FF82FF : Shifter (ST)
  • DFF000-DFF0DF : Paula (AMIGA)


file  mem68.h
 68k memory and IO manager header.

Memory access flags for reg68.chk (debug mode only).

#define READ_68   1
 Memory location has been read.

#define WRITTEN_68   2
 Memory location has been written.

#define EXECUTED_68   4
 Memory location has been executed.

#define BREAKED_68   8
 Memory location has emulator-breakpoint.

Memory/IO quick access tables.

#define ISIO68(ADDR)   ((ADDR)&0x800000)
 Test for direct memory access or IO quick table access.

memrfunc68_t read_mem_jmp_l [256]
 Read long.

memrfunc68_t read_mem_jmp_w [256]
 Read word.

memrfunc68_t read_mem_jmp_b [256]
 Read byte.

memwfunc68_t write_mem_jmp_l [256]
 Write long.

memwfunc68_t write_mem_jmp_w [256]
 Write word.

memwfunc68_t write_mem_jmp_b [256]
 Write byte.

68K onboard memory access.

#define read_B(ADDR)   read_68000mem_b(ADDR)
 Read memory byte.

#define read_W(ADDR)   read_68000mem_w(ADDR)
 Read memory word.

#define read_L(ADDR)   read_68000mem_l(ADDR)
 Read memory long.

#define write_B(ADDR, VAL)   write_68000mem_b(ADDR,VAL)
 Write memory byte.

#define write_W(ADDR, VAL)   write_68000mem_w(ADDR,VAL)
 Write memory word.

#define write_L(ADDR, VAL)   write_68000mem_l(ADDR,VAL)
 Write memory long.

u32 read_68000mem_b (u32 addr)
 Read memory byte.

u32 read_68000mem_w (u32 addr)
 Read memory word.

u32 read_68000mem_l (u32 addr)
 Read memory long.

void write_68000mem_b (u32 addr, u32 v)
 Write memory byte.

void write_68000mem_w (u32 addr, u32 v)
 Write memory word.

void write_68000mem_l (u32 addr, u32 v)
 Write memory long.

Instruction read.

s32 get_nextw (void)
 Decode word and update PC.

s32 get_nextl (void)
 Decode long and update PC.

Stack access.

void pushl (s32 v)
 Push long.

void pushw (s32 v)
 Push word.

s32 popl (void)
 Pop long.

s32 popw (void)
 Pop word.


void EMU68memory_init (void)
 Init memory quick access table.

void EMU68memory_reset (void)
 Reset memory quick access table.

void EMU68memory_new_area (u8 area, memrfunc68_t *read_bwl, memwfunc68_t *write_bwl)
 Add a new memory access control area (for new IO).

void EMU68memory_reset_area (u8 area)
 Reset memory access control area to default state.

Function Documentation

void EMU68memory_init void   ) 

Init memory quick access table.

The EMU68memory_init() function must be call at init time. Currently this function only call the EMU68memory_reset() function.

See also:

void EMU68memory_reset void   ) 

Reset memory quick access table.

The EMU68memory_reset() function restores all memory access to default. All mapped IO will be discard and replace by onboard memory access.

void EMU68memory_new_area u8  area,
memrfunc68_t read_bwl,
memwfunc68_t write_bwl

Add a new memory access control area (for new IO).

area Which area (bit 16 to 23 of address) to change.
read_bwl Read function table (byte, word and long in this order)
write_bwl idem read_bwl for write access.
See also:

void EMU68memory_reset_area u8  area  ) 

Reset memory access control area to default state.

See also: